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Microdeletion Gene Syndromes

By Nina N. Powell-Hamilton, MD, Clinical Assistant Professor of Pediatrics ;Medical Geneticist , Sidney Kimmel Medical College at Thomas Jefferson University;Nemours/Alfred I. duPont Hospital for Children

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Microdeletion syndromes are disorders caused by microscopic and submicroscopic deletions or duplications of contiguous genes on particular parts of chromosomes. Postnatal diagnosis is suspected by clinical appearance and confirmed by fluorescent in situ hybridization and chromosomal microarray analysis.

Microdeletion syndromes differ from chromosomal deletion syndromes in that deletion syndromes are usually visible on karyotyping because of their larger size (typically > 5 megabases), whereas the abnormalities in microdeletion syndromes involve smaller segments (typically 1 to 3 megabases) and are detectable only with fluorescent probes (fluorescent in situ hybridization) and microarray analysis. A given gene segment can be deleted or duplicated (termed a reciprocal duplication). The clinical effects of microscopic reciprocal duplications tend to be similar but less severe than those of deletions involving the same segment. The term contiguous gene syndrome encompasses both microdeletion syndromes and contiguous abnormalities visible on karyotyping.

Most clinically significant microdeletions and duplications seem to occur sporadically; however, mildly affected parents may be diagnosed when parental testing is done after a child is found to have an abnormality. Numerous syndromes have been identified, with widely varying manifestations (see Table: Examples of Microdeletion Syndromes).

Examples of Microdeletion Syndromes


Chromosomal Deletion


Alagille syndrome


Cholestasis, bile duct paucity, cardiac anomalies, pulmonary artery stenosis, butterfly vertebrae, posterior embryotoxon of the eye

Angelman syndrome

Maternal chromosome at 15q11

Seizures, puppet-like ataxia, frequent laughter, hand flapping, severe intellectual disability

DiGeorge syndrome (DiGeorge anomaly, velocardiofacial syndrome, pharyngeal pouch syndrome, thymic aplasia)


Hypoplasia or lack of thymus and parathyroids, cardiac anomalies, cleft palate, intellectual disability, psychiatric problems

Langer-Giedion syndrome (trichorhinophalangeal syndrome type II)


Exostosis, cone epiphyses, sparse hair, bulbous nose, hearing loss, intellectual disability

Miller-Dieker syndrome


Lissencephaly; short, upturned nose; severe growth retardation; seizures; severe intellectual disability

Paternal chromosome at 15q11

In infancy: Hypotonia, poor feeding, failure to thrive

In childhood and adolescence: Obesity, hypogonadism, small hands and feet, intellectual disability, obsessive-compulsive behaviors

Rubinstein-Taybi syndrome


Broad thumbs and large toes, prominent nose and columella, intellectual disability

Smith-Magenis syndrome


Brachycephaly, midfacial hypoplasia, prognathism, hoarse voice, short stature, intellectual disability

Williams syndrome


Aortic stenosis, intellectual disability, elfin facies, transient hypercalcemia in infants

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